A small-sized mobile camera is installed in a camera-equipped mobile terminal. In this small-sized mobile camera, an auto focus (AF) lens holder driving device is used. VCM systems using a voice coil motor (VCM) are known as a driving mechanism (actuator) used for the above-mentioned AF lens holder driving device. An AF lens holder driving device of the VCM type includes a magnetic circuit composed of a driving coil, a yoke and a permanent magnet as a driving mechanism (actuator). The driving mechanism of the VCM type is roughly categorized into the driving mechanism of “moving coil type” and the driving mechanism of “moving magnet type.”
An AF lens holder driving device of the VCM type employs a spring member (elastic member) that supports a columnar movable part including a lens (a lens and a lens holder) such that the movable part is displaceable in the light axis direction (center axis direction) in a state where the position of the movable part in the radial direction with respect to the fixing part is set. It is to be noted that the movable part is also referred to as moving body or movable body, and the fixing part is also referred to as fixing member, supporting body, housing, or fixing body. The above-mentioned driving mechanism is provided in the movable part (moving body) and the fixing part (fixing member; supporting body).
As the above-mentioned spring member (elastic member), in general, a pair of leaf springs which are provided on the both sides in the light axis direction of a lens holder (columnar movable part; moving body) that holds a lens assembly (lens barrel) are used. The pair of leaf springs supports the lens holder (columnar movable part; moving body) such that the lens holder is displaceable in the light axis direction in a state where the position in the radial direction of the lens holder is set with respect to the housing (cylindrical fixing part; fixing member; supporting body) disposed at the periphery thereof. One of the pair of leaf springs is referred to as upper leaf spring, and the other is referred to as lower leaf spring.
It is to be noted that the upper leaf spring is also referred to as front spring or front spring member, and the lower leaf spring is also referred to as rear spring or rear spring member.
With the above-mentioned configuration, in an AF lens holder driving device of the VCM type, the restoration force (biasing force) of the leaf spring (spring member) and the thrust (driving force) of the driving mechanism are balanced, and the movable part (moving body) is moved to a predetermined position (target position) in the light axis direction. In the AF lens holder driving device of the VCM type having such a configuration, the movable part (moving body) is supported with the leaf spring (spring member) with respect to the fixing part (fixing member; housing; supporting body), and therefore the movable part (moving body) is vibrated more than necessary by driving of the movable part (moving body), or by vibration, impact and the like from the outside.
Conventionally, various measures against such a problem have been proposed.
For example, in PTL 1, a buffer member composed of elastic resin is disposed at a leaf spring in which a plurality of cutout grooves are provided and a coupling part of the lens holder and the fixing member is formed. The buffer member is disposed in a region around the connection portion of the lens holder and the leaf spring, and in a region around the connection portion of the fixing member and the leaf spring.
In addition, in PTL 2, damping agent is applied to a spring including an outer ring, an inner ring and an elastic coupling part for coupling the rings. The damping agent is applied at a portion nearer to the inner ring of the elastic coupling part.
Further, in PTL 3, a buffer member having viscoelasticity is provided to a front spring member that is connected to a front end portion of a moving body in the lens light axis direction and a supporting body, and includes a supporting body coupling part, a moving body coupling part, and an arm part configured to connect the coupling parts. The buffer member is provided at only a part that extends between the moving body coupling part and a portion nearer to the connecting part of the arm part with the supporting body coupling part than the connecting part of the arm part with the moving body coupling part in the arm part, in portions that bridge the arm part.
Furthermore, in PTL 4, a spring member that connects a movable body and a fixing body is provided with a buffer member having viscoelasticity that reduces the vibration time of the movable body by absorbing the vibration of the movable body with respect to the fixing body in the light axis direction. At the installation position of the buffer member, a protrusion and/or a recess serving as a guide of the installation range of the buffer member is formed. The spring member includes a movable side fixing part that is fixed to the movable body, a fixation side fixing part that is fixed to the fixing body, and an arm part that connects the movable side fixing part and the fixation side fixing part. One end of the arm part which is connected with the movable side fixing part is the top end of the arm part, and the other end of the arm part which is connected with the fixation side fixing part of the arm part is the base end. The buffer member is provided at least one of the following portions: a portion extending between the movable side fixing part and the fixation side fixing part, a portion extending between parts of the arm part except for the top side and the movable side fixing part, a portion extending between parts of the arm part except for the base end side and the fixation side fixing part, a portion extending between the movable body and the fixation side fixing part, a portion extending between the fixing body and the movable side fixing part, a portion extending between parts of the arm part except for the end side and the movable body, a portion extending between parts of the arm part except for the base end side and the fixing body, and a portion extending between the movable body and the fixing body.
In addition, conventionally, the lens position is controlled by feedback control to improve the focusing accuracy (see, for example, PTL 5). The image pickup device lens disclosed in PTL 5 includes a driving device for adjusting the lens position, and a position detection device for detecting the lens position. A focus control circuit that is installed in the image pickup device includes a feedback equalizer that generates a driving signal for aligning the lens position with the target position based on the difference between the lens position that is specified with the output signal of the position detection device and a target position of the lens that is externally set, and controls the driving device.